Problem: Solve for $t$ : $30 + t = 23$
Answer: Subtract $30$ from both sides: $ \begin{eqnarray} \\ 30 + t &=& 23 \\ \\ {-30} && {-30} \end{eqnarray} $ $ \begin{eqnarray} \hphantom{30 + t} &\hphantom{=}& \hphantom{23} \\ t &=& 23 {- 30} \\ \end{eqnarray} $ Simplify. $ t = -7$